JUC 常用 4 大并發(fā)工具類
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來源 | www.cnblogs.com/flower-dance/p/13714006.html
什么是JUC? 4大常用并發(fā)工具類: CountDownLatch: CyclicBarrier: Semaphore: Exchanger:
什么是JUC?
JUC就是java.util.concurrent包,這個(gè)包俗稱JUC,里面都是解決并發(fā)問題的一些東西
該包的位置位于java下面的rt.jar包下面
4大常用并發(fā)工具類:
CountDownLatch
CyclicBarrier
Semaphore
ExChanger
CountDownLatch:
CountDownLatch,俗稱閉鎖,作用是類似加強(qiáng)版的Join,是讓一組線程等待其他的線程完成工作以后才執(zhí)行
就比如在啟動(dòng)框架服務(wù)的時(shí)候,我們主線程需要在環(huán)境線程初始化完成之后才能啟動(dòng),這時(shí)候我們就可以實(shí)現(xiàn)使用CountDownLatch來完成
/**
* Constructs a {@code CountDownLatch} initialized with the given count.
*
* @param count the number of times {@link #countDown} must be invoked
* before threads can pass through {@link #await}
* @throws IllegalArgumentException if {@code count} is negative
*/
public CountDownLatch(int count) {
if (count < 0) throw new IllegalArgumentException("count < 0");
this.sync = new Sync(count);
}
在源碼中可以看到,創(chuàng)建CountDownLatch時(shí),需要傳入一個(gè)int類型的參數(shù),將決定在執(zhí)行次扣減之后,等待的線程被喚醒
通過這個(gè)類圖就可以知道其實(shí)CountDownLatch并沒有多少東西
方法介紹:
CountDownLatch:初始化方法
await:等待方法,同時(shí)帶參數(shù)的是超時(shí)重載方法
countDown:每執(zhí)行一次,計(jì)數(shù)器減一,就是初始化傳入的數(shù)字,也代表著一個(gè)線程完成了任務(wù)
getCount:獲取當(dāng)前值
toString:這個(gè)就不用說了
里面的Sync是一個(gè)內(nèi)部類,外面的方法其實(shí)都是操作這個(gè)內(nèi)部類的,這個(gè)內(nèi)部類繼承了AQS,實(shí)現(xiàn)的標(biāo)準(zhǔn)方法,AQS將在后面的章節(jié)寫
主線程中創(chuàng)建CountDownLatch(3),然后主線程await阻塞,然后線程A,B,C各自完成了任務(wù),調(diào)用了countDown,之后,每個(gè)線程調(diào)用一次計(jì)數(shù)器就會(huì)減一,初始是3,然后A線程調(diào)用后變成2,B線程調(diào)用后變成1,C線程調(diào)用后,變成0,這時(shí)就會(huì)喚醒正在await的主線程,然后主線程繼續(xù)執(zhí)行
說一千道一萬(wàn),不如代碼寫幾行,上代碼:
休眠工具類,之后的代碼都會(huì)用到
package org.dance.tools;
import java.util.concurrent.TimeUnit;
/**
* 類說明：線程休眠輔助工具類
*/
public class SleepTools {
/**
* 按秒休眠
* @param seconds 秒數(shù)
*/
public static final void second(int seconds) {
try {
TimeUnit.SECONDS.sleep(seconds);
} catch (InterruptedException e) {
}
}
/**
* 按毫秒數(shù)休眠
* @param seconds 毫秒數(shù)
*/
public static final void ms(int seconds) {
try {
TimeUnit.MILLISECONDS.sleep(seconds);
} catch (InterruptedException e) {
}
}
}
package org.dance.day2.util;
import org.dance.tools.SleepTools;
import java.util.concurrent.CountDownLatch;
/**
* CountDownLatch的使用,有五個(gè)線程,6個(gè)扣除點(diǎn)
* 扣除完成后主線程和業(yè)務(wù)線程,才能執(zhí)行工作
* 扣除點(diǎn)一般都是大于等于需要初始化的線程的
* @author ZYGisComputer
*/
public class UseCountDownLatch {
/**
* 設(shè)置為6個(gè)扣除點(diǎn)
*/
static CountDownLatch countDownLatch = new CountDownLatch(6);
/**
* 初始化線程
*/
private static class InitThread implements Runnable {
@Override
public void run() {
System.out.println("thread_" + Thread.currentThread().getId() + " ready init work .....");
// 執(zhí)行扣減 扣減不代表結(jié)束
countDownLatch.countDown();
for (int i = 0; i < 2; i++) {
System.out.println("thread_" + Thread.currentThread().getId() + ".....continue do its work");
}
}
}
/**
* 業(yè)務(wù)線程
*/
private static class BusiThread implements Runnable {
@Override
public void run() {
// 業(yè)務(wù)線程需要在等初始化完畢后才能執(zhí)行
try {
countDownLatch.await();
for (int i = 0; i < 3; i++) {
System.out.println("BusiThread " + Thread.currentThread().getId() + " do business-----");
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
// 創(chuàng)建單獨(dú)的初始化線程
new Thread(){
@Override
public void run() {
SleepTools.ms(1);
System.out.println("thread_" + Thread.currentThread().getId() + " ready init work step 1st.....");
// 扣減一次
countDownLatch.countDown();
System.out.println("begin stop 2nd.....");
SleepTools.ms(1);
System.out.println("thread_" + Thread.currentThread().getId() + " ready init work step 2nd.....");
// 扣減一次
countDownLatch.countDown();
}
}.start();
// 啟動(dòng)業(yè)務(wù)線程
new Thread(new BusiThread()).start();
// 啟動(dòng)初始化線程
for (int i = 0; i <= 3; i++) {
new Thread(new InitThread()).start();
}
// 主線程進(jìn)入等待
try {
countDownLatch.await();
System.out.println("Main do ites work.....");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
返回結(jié)果:
thread_13 ready init work .....
thread_13.....continue do its work
thread_13.....continue do its work
thread_14 ready init work .....
thread_14.....continue do its work
thread_14.....continue do its work
thread_15 ready init work .....
thread_15.....continue do its work
thread_11 ready init work step 1st.....
begin stop 2nd.....
thread_16 ready init work .....
thread_16.....continue do its work
thread_16.....continue do its work
thread_15.....continue do its work
thread_11 ready init work step 2nd.....
Main do ites work.....
BusiThread 12 do business-----
BusiThread 12 do business-----
BusiThread 12 do business-----
通過返回結(jié)果就可以很直接的看到業(yè)務(wù)線程是在初始化線程完全跑完之后,才開始執(zhí)行的
CyclicBarrier:
CyclicBarrier,俗稱柵欄鎖,作用是讓一組線程到達(dá)某個(gè)屏障,被阻塞,一直到組內(nèi)的最后一個(gè)線程到達(dá),然后屏障開放,接著,所有的線程繼續(xù)運(yùn)行
這個(gè)感覺和CountDownLatch有點(diǎn)相似,但是其實(shí)是不一樣的,所謂的差別,將在下面詳解
CyclicBarrier的構(gòu)造參數(shù)有兩個(gè)
/**
* Creates a new {@code CyclicBarrier} that will trip when the
* given number of parties (threads) are waiting upon it, and
* does not perform a predefined action when the barrier is tripped.
*
* @param parties the number of threads that must invoke {@link #await}
* before the barrier is tripped
* @throws IllegalArgumentException if {@code parties} is less than 1
*/
public CyclicBarrier(int parties) {
this(parties, null);
}
/**
* Creates a new {@code CyclicBarrier} that will trip when the
* given number of parties (threads) are waiting upon it, and which
* will execute the given barrier action when the barrier is tripped,
* performed by the last thread entering the barrier.
*
* @param parties the number of threads that must invoke {@link #await}
* before the barrier is tripped
* @param barrierAction the command to execute when the barrier is
* tripped, or {@code null} if there is no action
* @throws IllegalArgumentException if {@code parties} is less than 1
*/
public CyclicBarrier(int parties, Runnable barrierAction) {
if (parties <= 0) throw new IllegalArgumentException();
this.parties = parties;
this.count = parties;
this.barrierCommand = barrierAction;
}
很明顯能感覺出來,上面的構(gòu)造參數(shù)調(diào)用了下面的構(gòu)造參數(shù),是一個(gè)構(gòu)造方法重載
首先這個(gè)第一個(gè)參數(shù)也樹Int類型的,傳入的是執(zhí)行線程的個(gè)數(shù),這個(gè)數(shù)量和CountDownLatch不一樣,這個(gè)數(shù)量是需要和線程數(shù)量吻合的,CountDownLatch則不一樣,CountDownLatch可以大于等于,而CyclicBarrier只能等于,然后是第二個(gè)參數(shù),第二個(gè)參數(shù)是barrierAction,這個(gè)參數(shù)是當(dāng)屏障開放后,執(zhí)行的任務(wù)線程,如果當(dāng)屏障開放后需要執(zhí)行什么任務(wù),可以寫在這個(gè)線程中
主線程創(chuàng)建CyclicBarrier(3,barrierAction),然后由線程開始執(zhí)行,線程A,B執(zhí)行完成后都調(diào)用了await,然后他們都在一個(gè)屏障前阻塞者,需要等待線程C也,執(zhí)行完成,調(diào)用await之后,然后三個(gè)線程都達(dá)到屏障后,屏障開放,然后線程繼續(xù)執(zhí)行,并且barrierAction在屏障開放的一瞬間也開始執(zhí)行
上代碼:
package org.dance.day2.util;
import org.dance.tools.SleepTools;
import java.util.Map;
import java.util.Random;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CyclicBarrier;
/**
* CyclicBarrier的使用
*
* @author ZYGisComputer
*/
public class UseCyclicBarrier {
/**
* 存放子線程工作結(jié)果的安全容器
*/
private static ConcurrentHashMap<String, Long> resultMap = new ConcurrentHashMap<>();
private static CyclicBarrier cyclicBarrier = new CyclicBarrier(5,new CollectThread());
/**
* 結(jié)果打印線程
* 用來演示CyclicBarrier的第二個(gè)參數(shù),barrierAction
*/
private static class CollectThread implements Runnable {
@Override
public void run() {
StringBuffer result = new StringBuffer();
for (Map.Entry<String, Long> workResult : resultMap.entrySet()) {
result.append("[" + workResult.getValue() + "]");
}
System.out.println("the result = " + result);
System.out.println("do other business.....");
}
}
/**
* 工作子線程
* 用于CyclicBarrier的一組線程
*/
private static class SubThread implements Runnable {
@Override
public void run() {
// 獲取當(dāng)前線程的ID
long id = Thread.currentThread().getId();
// 放入統(tǒng)計(jì)容器中
resultMap.put(String.valueOf(id), id);
Random random = new Random();
try {
if (random.nextBoolean()) {
Thread.sleep(1000 + id);
System.out.println("Thread_"+id+"..... do something");
}
System.out.println(id+" is await");
cyclicBarrier.await();
Thread.sleep(1000+id);
System.out.println("Thread_"+id+".....do its business");
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
for (int i = 0; i <= 4; i++) {
Thread thread = new Thread(new SubThread());
thread.start();
}
}
}
返回結(jié)果:
11 is await
14 is await
15 is await
Thread_12..... do something
12 is await
Thread_13..... do something
13 is await
the result = [11][12][13][14][15]
do other business.....
Thread_11.....do its business
Thread_12.....do its business
Thread_13.....do its business
Thread_14.....do its business
Thread_15.....do its business
通過返回結(jié)果可以看出前面的11 14 15三個(gè)線程沒有進(jìn)入if語(yǔ)句塊,在執(zhí)行到await的時(shí)候進(jìn)入了等待,而另外12 13兩個(gè)線程進(jìn)入到了if語(yǔ)句塊當(dāng)中,多休眠了1秒多,然后當(dāng)5個(gè)線程同時(shí)到達(dá)await的時(shí)候,屏障開放,執(zhí)行了barrierAction線程,然后線程組繼續(xù)執(zhí)行
解釋一下CountDownLatch和CyclicBarrier的卻別吧!
首先就是CountDownLatch的構(gòu)造參數(shù)傳入的數(shù)量一般都是大于等于線程,數(shù)量的,因?yàn)樗怯械谌娇刂频?可以扣減多次,然后就是CyclicBarrier的構(gòu)造參數(shù)第一個(gè)參數(shù)傳入的數(shù)量一定是等于線程的個(gè)數(shù)的,因?yàn)樗怯梢唤M線程自身控制的
區(qū)別
CountDownLatch CyclicBarrier
控制 第三方控制 自身控制
傳入數(shù)量 大于等于線程數(shù)量 等于線程數(shù)量
Semaphore:
Semaphore,俗稱信號(hào)量,作用于控制同時(shí)訪問某個(gè)特定資源的線程數(shù)量,用在流量控制
一說特定資源控制,那么第一時(shí)間就想到了數(shù)據(jù)庫(kù)連接..
之前用等待超時(shí)模式寫了一個(gè)數(shù)據(jù)庫(kù)連接池,打算用這個(gè)Semaphone也寫一個(gè)
/**
* Creates a {@code Semaphore} with the given number of
* permits and nonfair fairness setting.
*
* @param permits the initial number of permits available.
* This value may be negative, in which case releases
* must occur before any acquires will be granted.
*/
public Semaphore(int permits) {
sync = new NonfairSync(permits);
}
在源碼中可以看到在構(gòu)建Semaphore信號(hào)量的時(shí)候,需要傳入許可證的數(shù)量,這個(gè)數(shù)量就是資源的最大允許的訪問的線程數(shù)
接下里用信號(hào)量實(shí)現(xiàn)一個(gè)數(shù)據(jù)庫(kù)連接池
連接對(duì)象
package org.dance.day2.util.pool;
import org.dance.tools.SleepTools;
import java.sql.*;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.Executor;
/**
* 數(shù)據(jù)庫(kù)連接
* @author ZYGisComputer
*/
public class SqlConnection implements Connection {
/**
* 獲取數(shù)據(jù)庫(kù)連接
* @return
*/
public static final Connection fetchConnection(){
return new SqlConnection();
}
@Override
public void commit() throws SQLException {
SleepTools.ms(70);
}
@Override
public Statement createStatement() throws SQLException {
SleepTools.ms(1);
return null;
}
@Override
public PreparedStatement prepareStatement(String sql) throws SQLException {
return null;
}
@Override
public CallableStatement prepareCall(String sql) throws SQLException {
return null;
}
@Override
public String nativeSQL(String sql) throws SQLException {
return null;
}
@Override
public void setAutoCommit(boolean autoCommit) throws SQLException {
}
@Override
public boolean getAutoCommit() throws SQLException {
return false;
}
@Override
public void rollback() throws SQLException {
}
@Override
public void close() throws SQLException {
}
@Override
public boolean isClosed() throws SQLException {
return false;
}
@Override
public DatabaseMetaData getMetaData() throws SQLException {
return null;
}
@Override
public void setReadOnly(boolean readOnly) throws SQLException {
}
@Override
public boolean isReadOnly() throws SQLException {
return false;
}
@Override
public void setCatalog(String catalog) throws SQLException {
}
@Override
public String getCatalog() throws SQLException {
return null;
}
@Override
public void setTransactionIsolation(int level) throws SQLException {
}
@Override
public int getTransactionIsolation() throws SQLException {
return 0;
}
@Override
public SQLWarning getWarnings() throws SQLException {
return null;
}
@Override
public void clearWarnings() throws SQLException {
}
@Override
public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
return null;
}
@Override
public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
return null;
}
@Override
public Map<String, Class<?>> getTypeMap() throws SQLException {
return null;
}
@Override
public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
}
@Override
public void setHoldability(int holdability) throws SQLException {
}
@Override
public int getHoldability() throws SQLException {
return 0;
}
@Override
public Savepoint setSavepoint() throws SQLException {
return null;
}
@Override
public Savepoint setSavepoint(String name) throws SQLException {
return null;
}
@Override
public void rollback(Savepoint savepoint) throws SQLException {
}
@Override
public void releaseSavepoint(Savepoint savepoint) throws SQLException {
}
@Override
public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
return null;
}
@Override
public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
return null;
}
@Override
public Clob createClob() throws SQLException {
return null;
}
@Override
public Blob createBlob() throws SQLException {
return null;
}
@Override
public NClob createNClob() throws SQLException {
return null;
}
@Override
public SQLXML createSQLXML() throws SQLException {
return null;
}
@Override
public boolean isValid(int timeout) throws SQLException {
return false;
}
@Override
public void setClientInfo(String name, String value) throws SQLClientInfoException {
}
@Override
public void setClientInfo(Properties properties) throws SQLClientInfoException {
}
@Override
public String getClientInfo(String name) throws SQLException {
return null;
}
@Override
public Properties getClientInfo() throws SQLException {
return null;
}
@Override
public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
return null;
}
@Override
public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
return null;
}
@Override
public void setSchema(String schema) throws SQLException {
}
@Override
public String getSchema() throws SQLException {
return null;
}
@Override
public void abort(Executor executor) throws SQLException {
}
@Override
public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
}
@Override
public int getNetworkTimeout() throws SQLException {
return 0;
}
@Override
public <T> T unwrap(Class<T> iface) throws SQLException {
return null;
}
@Override
public boolean isWrapperFor(Class<?> iface) throws SQLException {
return false;
}
}
連接池對(duì)象
package org.dance.day2.util.pool;
import java.sql.Connection;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.concurrent.Semaphore;
/**
* 使用信號(hào)量控制數(shù)據(jù)庫(kù)的鏈接和釋放
*
* @author ZYGisComputer
*/
public class DBPoolSemaphore {
/**
* 池容量
*/
private final static int POOL_SIZE = 10;
/**
* useful 代表可用連接
* useless 代表已用連接
* 為什么要使用兩個(gè)Semaphore呢?是因?yàn)?在連接池中不只有連接本身是資源,空位也是資源,也需要記錄
*/
private final Semaphore useful, useless;
/**
* 連接池
*/
private final static LinkedList<Connection> POOL = new LinkedList<>();
/**
* 使用靜態(tài)塊初始化池
*/
static {
for (int i = 0; i < POOL_SIZE; i++) {
POOL.addLast(SqlConnection.fetchConnection());
}
}
public DBPoolSemaphore() {
// 初始可用的許可證等于池容量
useful = new Semaphore(POOL_SIZE);
// 初始不可用的許可證容量為0
useless = new Semaphore(0);
}
/**
* 獲取數(shù)據(jù)庫(kù)連接
*
* @return 連接對(duì)象
*/
public Connection takeConnection() throws InterruptedException {
// 可用許可證減一
useful.acquire();
Connection connection;
synchronized (POOL) {
connection = POOL.removeFirst();
}
// 不可用許可證數(shù)量加一
useless.release();
return connection;
}
/**
* 釋放鏈接
*
* @param connection 連接對(duì)象
*/
public void returnConnection(Connection connection) throws InterruptedException {
if(null!=connection){
// 打印日志
System.out.println("當(dāng)前有"+useful.getQueueLength()+"個(gè)線程等待獲取連接,,"
+"可用連接有"+useful.availablePermits()+"個(gè)");
// 不可用許可證減一
useless.acquire();
synchronized (POOL){
POOL.addLast(connection);
}
// 可用許可證加一
useful.release();
}
}
}
測(cè)試類:
package org.dance.day2.util.pool;
import org.dance.tools.SleepTools;
import java.sql.Connection;
import java.util.Random;
/**
* 測(cè)試Semaphore
* @author ZYGisComputer
*/
public class UseSemaphore {
/**
* 連接池
*/
public static final DBPoolSemaphore pool = new DBPoolSemaphore();
private static class BusiThread extends Thread{
@Override
public void run() {
// 隨機(jī)數(shù)工具類 為了讓每個(gè)線程持有連接的時(shí)間不一樣
Random random = new Random();
long start = System.currentTimeMillis();
try {
Connection connection = pool.takeConnection();
System.out.println("Thread_"+Thread.currentThread().getId()+
"_獲取數(shù)據(jù)庫(kù)連接耗時(shí)["+(System.currentTimeMillis()-start)+"]ms.");
// 模擬使用連接查詢數(shù)據(jù)
SleepTools.ms(100+random.nextInt(100));
System.out.println("查詢數(shù)據(jù)完成歸還連接");
pool.returnConnection(connection);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
for (int i = 0; i < 50; i++) {
BusiThread busiThread = new BusiThread();
busiThread.start();
}
}
}
測(cè)試返回結(jié)果:
Thread_11_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[0]ms.
Thread_12_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[0]ms.
Thread_13_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[0]ms.
Thread_14_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[0]ms.
Thread_15_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[0]ms.
Thread_16_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[0]ms.
Thread_17_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[0]ms.
Thread_18_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[0]ms.
Thread_19_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[0]ms.
Thread_20_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[0]ms.
查詢數(shù)據(jù)完成歸還連接
當(dāng)前有40個(gè)線程等待獲取連接,,可用連接有0個(gè)
Thread_21_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[112]ms.
查詢數(shù)據(jù)完成歸還連接
...................
查詢數(shù)據(jù)完成歸還連接
當(dāng)前有2個(gè)線程等待獲取連接,,可用連接有0個(gè)
Thread_59_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[637]ms.
查詢數(shù)據(jù)完成歸還連接
當(dāng)前有1個(gè)線程等待獲取連接,,可用連接有0個(gè)
Thread_60_獲取數(shù)據(jù)庫(kù)連接耗時(shí)[660]ms.
查詢數(shù)據(jù)完成歸還連接
當(dāng)前有0個(gè)線程等待獲取連接,,可用連接有0個(gè)
查詢數(shù)據(jù)完成歸還連接
...................
當(dāng)前有0個(gè)線程等待獲取連接,,可用連接有8個(gè)
查詢數(shù)據(jù)完成歸還連接
當(dāng)前有0個(gè)線程等待獲取連接,,可用連接有9個(gè)
通過執(zhí)行結(jié)果可以很明確的看到,一上來就有10個(gè)線程獲取到了連接,,然后后面的40個(gè)線程進(jìn)入阻塞,然后只有釋放鏈接之后,等待的線程就會(huì)有一個(gè)拿到,然后越后面的線程等待的時(shí)間就越長(zhǎng),然后一直到所有的線程執(zhí)行完畢
最后打印的可用連接有九個(gè)不是因?yàn)樯倭艘粋€(gè)是因?yàn)樵卺尫胖按蛴〉?不是錯(cuò)誤
從結(jié)果中可以看到,我們對(duì)連接池中的資源的到了控制,這就是信號(hào)量的流量控制
Exchanger:
Exchanger,俗稱交換器,用于在線程之間交換數(shù)據(jù),但是比較受限,因?yàn)橹荒軆蓚€(gè)線程之間交換數(shù)據(jù)
/**
* Creates a new Exchanger.
*/
public Exchanger() {
participant = new Participant();
}
這個(gè)構(gòu)造函數(shù)沒有什么好說的,也沒有入?yún)?只有在創(chuàng)建的時(shí)候指定一下需要交換的數(shù)據(jù)的泛型即可,下面看代碼
package org.dance.day2.util;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.Exchanger;
/**
* 線程之間交換數(shù)據(jù)
* @author ZYGisComputer
*/
public class UseExchange {
private static final Exchanger<Set<String>> exchanger = new Exchanger<>();
public static void main(String[] args) {
new Thread(){
@Override
public void run() {
Set<String> aSet = new HashSet<>();
aSet.add("A");
aSet.add("B");
aSet.add("C");
try {
Set<String> exchange = exchanger.exchange(aSet);
for (String s : exchange) {
System.out.println("aSet"+s);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}.start();
new Thread(){
@Override
public void run() {
Set<String> bSet = new HashSet<>();
bSet.add("1");
bSet.add("2");
bSet.add("3");
try {
Set<String> exchange = exchanger.exchange(bSet);
for (String s : exchange) {
System.out.println("bSet"+s);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}.start();
}
}
執(zhí)行結(jié)果:
bSetA
bSetB
bSetC
aSet1
aSet2
aSet3
通過執(zhí)行結(jié)果可以清晰的看到,兩個(gè)線程中的數(shù)據(jù)發(fā)生了交換,這就是Exchanger的線程數(shù)據(jù)交換了
以上就是JUC的4大常用并發(fā)工具類了
評(píng)論
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